This invention relates to a heating arrangement, and in particular to apparatus for preventing the formation of ice on a substrate that is exposed to an outdoor environment.
The ViaGard(trademark) heating system available from Raychem HTS provides a polymeric self regulating heater that may be embedded in driveways, pathways or steps, for example, so that heating can be supplied to prevent the formation of ice thereon, or to melt any fallen snow. Control of the ViaGard(trademark) heating system is effected by utilizing the outputs from sensors that are embedded in the substrate, for example a concrete slab, that detect the temperature and any moisture present in the substrate. Thus, when the sensed temperature is detected as being below predetermined values and in the presence of moisture, the electrical supply to the heater is switched on. There are weather conditions, however, in which the response of such a system is not good enough, resulting either in the heater being switched or kept on unnecessarily, or in not being switched on soon enough.
An object of the present invention to provide improved heating of an outdoor substrate to prevent or at least to alleviate the formation of ice thereon.
In accordance with one aspect of the present invention, there is provided apparatus for preventing the formation of ice on a substrate exposed to an outdoor environment, the apparatus comprising a sensor for measuring the temperature of the ambient air around the substrate, a sensor for measuring the temperature of the substrate, preferably a sensor for detecting the presence of moisture on the substrate, and a heater arranged to supply heat to the substrate in response to pre-arranged conditions dependent on the outputs of the said sensors.
In another aspect of the invention, the temperature and moisture sensing may be carried out on a test substrate and, under conditions conducive to the formation of ice thereon, heating may be applied to another, neighboring substrate on which the formation of ice is to be prevented. Furthermore, detection of conditions conducive to the formation of ice on one substrate may be arranged to provide heating to two or more neighboring substrates, which may be considered as susceptible to formation of ice thereon.
The substrate or substrates may be a pathway or driveway, especially if inclined, or steps, associated with a building, for example. The heating control of the present invention, however, may be applied to sports grounds, for example, where hot water pumped through pipes, which may be embedded in the ground, provides a preferred heater.
The output signals from the temperature sensors and from the moisture sensor may be supplied to an electronic control unit in which is stored an algorithm which has been predetermined so as to activate the heater of the apparatus under conditions regarded as conducive to the formation of ice.
In accordance with another aspect of the present invention, a method is provided for preventing ice formation on a substrate exposed to an outdoor environment. Heat is applied to the substrate in an amount dependent on pre-arranged conditions derived from measurement of the temperature of the ambient air around the substrate, the temperature of the substrate, and preferably the presence of moisture on the substrate.
The processing of the sensed parameters in the control unit can thus be arranged to lead to activation of the heating of the substrate prior to the occurrence of rain or snow. This contrasts with known ice protection systems, in which under certain conditions the heating is activated only after the formation of ice. For example, in the event of extremely cold weather, for example xe2x88x9215xc2x0 C., for several days without there being any snow, the substrate can freeze down to that low temperature. Should the air temperature then rise rapidly, for example up to zero degrees within a few hours, and should rain occur, the heating of the substrate will be slow to dispel the ice because of the thermal inertia that has to be overcome.
The control unit for the heater of the present invention can be arranged to take into account not only the absolute values of temperature and moisture, but also the rate of change of temperature, for example.
The apparatus may also comprise a sensor for measuring the relative humidity of the ambient air around the substrate, wherein activation of the heater is responsive to the output of the humidity sensor. Furthermore, the apparatus may comprise a sensor for measuring the pressure of the ambient air around the substrate, and activation of the heater may then be responsive to the output of the pressure sensor.
It will be appreciated that the time and/or the power output of the heater may be controlled in response to the measured parameters and/or their rate of change.
The moisture sensor is preferably one that itself is heated, so as to avoid false output signals therefrom. Advantageously, the amount of heat applied thereto is arranged to be substantially equal to heat loss therefrom to its surroundings. Thus, in accordance with another aspect of the present invention, a moisture sensor is heated by means of an electrical resistance heater, for example a self regulating or constant wattage heater cable, in such a way as to compensate for the heat loss of the sensor to the surrounding substrate and air. The ambient temperature is sensed by a separate temperature sensor. A proportional ambient sensing control algorithm is then used, such that the heater of the moisture sensor is switched on full (100% heating) at the minimum design temperature for the associated heating apparatus, for example xe2x88x9220xc2x0 C., and may be linearly reduced to zero percent (i.e. switched off) at a further predetermined temperature, for example +3xc2x0 C. The switching of the heating element may be controlled by a triac, a solid state relay, or an electromechanical relay, for example.
Weather conditions such as cold nights interspersed with warm days may give rise to unnecessary operation of the heater, that is to say, under conditions when in fact rain or snow leading to the formation of ice is not expected. Control of the heater may thus include an algorithm, whereby the requirement must also be met that the substrate has been sensed to be at less than a predetermined temperature, of say xe2x88x928xc2x0 C., for a minimum time, of say 24 hours, before the heater is activated.
Additionally or alternatively, control of the heater of the apparatus may be responsive to information received remotely, for example from a weather forecasting service.
Preferably, heating of the substrate is effected by a self regulating, preferably polymeric, electrical heater, which may advantageously be embedded in the substrate or other component to be heated. Electrical heating may alternatively be provided by a constant wattage heater. It is also envisaged, however, that the substrate may be heated by means of hot water, flowing through pipework.